It's a term they used back in the late 1800s to describe an all-purpose stage entertainer: a little music, a little hoofing, comedy, character roles, the guy who propped up the leading man and ingenue, the engine that kept a show moving. And in the past couple of years, Greg McCormick Allen has been the best local example of one?as Schultzy in Village Theatre's Show Boat and in the 5th Avenue's On the Town as Ozzie, the eager horndog among the three sailors enjoying a whirlwind WWII shore leave. What made the 5th's production work so wonderfully was its sense of period style, not just surface decoration but a savvy understanding of the theatrical traditions that made the show a hit in the first place?traditions that Allen embodies as winningly as any actor in town. ?Gavin Borchert